Molecular relationships in potentially hybridising species of the acropora 'palmata'-group

Student Report- University of Groningen 

Molecular relationships were investigated among the three Caribbean Acropora species Acropora palmata, A. cervicornis and A. prol4fera. To examen the possibility of interspecific hybndisation occurring in the field sequence analysis of rDNA ITS 1, ITS2 and the 5.8S coding region and Pax-C intron was performed. Phylogenetic analysis showed no or hardly any genetic structure and uncorrected pdistance showed a maximum of 9.84 % sequence difference for the total region (ITS! and 2, and 5.8S). In addition, variances calculated with Analysis of Molecular Variance showed no significant fraction of the total genetic variance being partitioned among species. These results may be correlated with interspecific hybridisation events - whether occurring at present or in the past. Results from other research projects involving morphological features, morphometrics and reproductive characters (Stockwell and Willis pers comm), spawning time (Szmant 1986) and fossil record (Budd Ct al. 1994) of these coral species, support this. However, the three Caribbean Acropora morphospecies could also have descended from a common ancestor and the sharing of similar sequence repeats may represent ancestral polymorphism. Whether speciation is occurring and the three species are diverging or merging is not known and questions concerning the mechanism behind the maintenance of different morphological features remain unclear.